The innovation relates to a holding device for circuit boards in plug-in units intended to receive electrical and electronic components in industrial electronic devices and including a front panel, with the circuit board being fastened to the rear of the front panel and perpendicularly thereto by means of at least two holding blocks.
The innovation is employed, in particular, in such plug-in units which are equipped with circuit boards; having larger dimensions and consequently also having larger front panels.
The firm, mechanical connection of a front panel with a circuit board with the aid of holding blocks is called a plug-in unit. Such a unit offers the advantage that the components of the circuit board can be firmly connected with operating and display elements on the face of the unit and the space requirement in the component carrier is fixed.
To fasten the circuit board to the front panel, a plug-in unit requires at least two fastening points. These fastening points lie at the corners of the circuit board and at the ends of the front panel; holding blocks provided with threaded holes serve as the fastening points in which engage fastening screws. To establish a connection, the front panel is screwed to the holding blocks from one side and the circuit board at a right angle thereto. The forces required to pull out the circuit board--in view of the multiple-prong connections employed, these may amount to up to 10 kiloponds--are transferred without difficulty by way of these double screw connections. Customarily, the fastening screws penetrating the front panel are hidden in or behind gripping strips and are therefore invisible.
It has now been found that the connection of circuit boards and front panels at two fastening points is not sufficient for circuit boards having large dimensions. High circuit boards additionally require lateral guidance between the fastening points and, moreover, the front panel requires a center support during insertion. To be able to control these transverse and pressure forces, it is known to provide one or two additional holding blocks between the two fastening points in the corners. However, this is a considerable disadvantage because in this central region of the front panel, it must be possible to install operating elements, measuring instruments or the like and additionally screw holes would be visible in a highly undesirable manner.